my nitrate level is at 20, nitrite is at 0, ammonia is at 0, ph levels are 8.2 or so. my sand is turning brownish i did some research and found that they are diatoms the brown algae. how do i get rid of them? is there a way besides vacuming the sand?

strong water movement . blow around the top layer of sand

what ever you have the water cant be stagnent ove the sand you can also try cucummbers starfish or snails

Are you topping up regularly? I found that i got it a lot when I let my salinity raise with too much evaporation and then put ro in to top up which lowered it too fast again.
I would try to maintain salinity levels constantly if youre not already and lower your nitrates if you can.

i had the same problem and it pissed me off i ended up starving the algae by getting a phosphate mat. i dont know the name of the product but with it did was suck up all the phosphates in the tank and in like 3 days my sand was pure white like when i bought it

If you have a predator tank, you could try to get a ray, such as a blue spot ray. If you can't keep predators, get some sand gobies 9such as golden head sleeper bobies). These fish will constantly turn over the sand and therefore prevent any diatoms from being able to grow.